(a) Field of the Invention
The present invention relates to a polyester fiber that can be applied to a fabric for an airbag, and particularly to a high strength and low modulus polyester fiber having superior mechanical properties, dimensional stability, packing properties, and the like, a method of preparing the same, and a fabric for an airbag using the same.
(b) Description of the Related Art
Generally, an airbag is an apparatus for protecting a driver and passengers by providing a gas into the airbag by exploding gunpowder so as to inflate the airbag after detecting a crash impact with an impact detecting sensor, when a driving car collides at a speed of about 40 km/h or more, and a structure of a conventional airbag system is depicted in FIG. 1.
As depicted in FIG. 1, conventional airbag system includes: an inflator 121 that generates a gas by ignition of a detonator 122; an airbag module 100 installed in a steering wheel 101 and including an airbag 124 that is expanded and unfolded toward a driver on the driver's seat by the generated gas; an impact sensor 130 that gives an impact signal when the car has crashed; and an electronic control module (ECM) 110 that ignites the detonator 122 of the inflator 121 according to the impact signal. In the airbag system, the impact sensor 130 detects the impact and sends the signal to the ECM when the car collides. At this time, the ECM 110 that received the signal ignites the detonator 122 and a gas generator in the inflator 121 is combusted. The combusted gas generator generates the gas rapidly and expands the airbag 124. The expanded airbag 124 contacts the front upper body of the driver and partially absorbs the impact load caused by the collision, and when the driver's head and chest go forward according to the law of inertia and smash against the airbag 124, it further absorbs the shock toward the driver by rapidly discharging the gas from the airbag through discharging holes formed on the airbag. Therefore, the airbag effectively absorbs the shock that is delivered to the driver, and can reduce secondary injuries at the time of a collision.
As disclosed above, an airbag for a car is prepared in a certain shape and is installed in the steering wheel, door roof rails, or side pillars of the car in a folded form so as to minimize its volume, and it is expanded and unfolded when the inflator 121 operates.
Therefore, it is very important that the airbag has folding properties and flexibility for reducing the shock to the occupant in addition to good mechanical properties of the fabric for maintaining the folding and packaging properties of the airbag effectively when it is installed in a car, preventing damage to and rupture of the airbag itself, providing good unfolding properties of the airbag cushion, and minimizing the impact provided to the occupant. However, an airbag fabric that can maintain superior air-tightness and flexibility for the occupant's safety, sufficiently endure the impact applied to the airbag, and be effectively installed in a car has not yet been suggested.
Previously, a polyamide fiber such as nylon 66 has been used as the raw material of the fiber for an airbag. However, nylon 66 has superior impact resistance but is inferior to polyester fiber in humid heat resistance, light resistance, and dimensional stability, and is expensive.
Meanwhile, Japanese patent publication No. Hei 04-214437 suggested a polyester fiber for reducing such defects. However, when the airbag was prepared by using a prior polyester fiber, it was difficult to install in a narrow space in a car because of its high modulus, and there was a limitation for maintaining sufficient mechanical and unfolding properties in severe conditions of high temperature and high humidity.
Therefore, it is needed to develop a fiber that maintains superior dimensional stability and gas barrier effect so as to be used for an airbag fabric, and also maintains flexibility for reducing the impact applied to passengers, the packing properties, and superior mechanical properties in the severe conditions of high temperature and high humidity.